1. Field of the Invention
The present invention relates to an organic light emitting diode (OLED) display device. More particularly, the present invention relates to an OLED display device having an improved storage capacitance, and a method of fabricating the same.
2. Discussion of the Related Art
As society has entered more of an information age, various types of display devices that represent all sorts of electrical signals as visual images have been rapidly developed. For example, a liquid crystal display (LCD) device and an organic light emitting diode (OLED) display device have been widely introduced and used as a substitute for a display device of cathode-ray tube type.
The OLED display device of new flat panel display devices is a self-emitting type. The OLED display device has excellent characteristics of a view angle, a contrast ratio and so on. Also, since the OLED display device does not require a backlight assembly, the OLED display device has low weight and low power consumption. Moreover, the OLED display device has advantages of a high response rate, a low production cost and so on. In addition, all elements of the OLED display device are a solid phase, the device is strong against an outer impact. Particularly, there is a big advantage in production cost. A fabricating process of the OLED display device is very simple and requires a deposition apparatus and an encapsulating apparatus.
In an active matrix type OLED device, a voltage for controlling an electric current of a pixel is charged in a storage capacitor such that a level of the electric current is maintained to a next frame.
FIG. 1 is a circuit diagram of one pixel region of the related art OLED display device.
As shown in FIG. 1, the OLED display device includes a gate line GL along a first direction, a data line DL along a second direction, a switching thin film transistor (TFT) Tsw, a storage capacitor Cst, a driving TFT Tdr, and an emitting diode E. The gate line GL and the data line DL cross each other to define a pixel region P.
The switching TFT Tsw is positioned at a crossing portion of the gate and data lines GL and DL and is connected to the gate and data line GL and DL. The driving TFT Tdr is electrically connected to the switching TFT Tsw.
The driving TFT Tdr and the storage capacitor Cst are connected to the switching TFT Tsw and a high level voltage VDD. The emitting diode E is connected to the driving TFT Tdr and a low level voltage VSS.
When the switching TFT Tsw is turned on by a gate signal applied through the gate line GL, a data signal from the data line DL is applied to the gate electrode of the driving TFT Tdr and an electrode of the storage capacitor Cst. When the driving TFT Tdr is turned on by the data signal, an electric current is supplied to the emitting diode E from the high level voltage VDD. As a result, the emitting diode E emits light. In this case, when the driving TFT Tdr is turned on, a level of an electric current to the emitting diode E is determined such that the emitting diode E can produce a gray scale.
The storage capacitor Cst serves to maintain the voltage of the gate electrode of the driving TFT Tdr when the switching TFT Tsw is turned off. Accordingly, even if the switching TFT Tsw is turned off, a level of an electric current to the emitting diode E is maintained to next frame.
To produce a high resolution display device, a number of pixel regions P in a unit area should be increased. Namely, in the high resolution display device, a size of one pixel region P is decreased.
When the size of one pixel region P is decreased, a size of the storage capacitor Cst is also decreased such that a storage capacitance is decreased.
When a size of the storage capacitor Cst is increased to provide high storage capacitance, the aperture ratio is reduced.